1. Field of the Invention
The present invention relates to toner particles for developing electrostatic charge images in image forming methods such as electrophotography and electrostatic printing, and also relates to a toner particle manufacturing method for manufacturing toner particles for forming toner images in image forming methods of the toner jet method.
2. Description of the Related Art
Various known electrophotography methods have been proposed in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910, and Japanese Patent Publication No. 43-24748. There are two developing methods in electrophotography, the dry developing method and the wet developing method. This dry developing method can be divided into two methods; a method which uses a two-component developer and a method which uses a one-component developer.
The toner particles used for the dry developing method are generally fine particles of colored resin, including as the main component binder resin and coloring agent, and the particle diameter thereof is generally within a range between 8 to 30 .mu.m. A common manufacturing method for manufacturing such toner particles is the so-called pulverizing method, wherein binder resin, a coloring agent such as pigment and/or a magnetic substance, waxes, etc., are melt-kneaded, the kneaded material is cooled, the cooled kneaded material is pulverized, and the pulverized material is classified, thereby creating toner particles. The form of toner particles formed by this pulverizing method is a generally irregular shape with corners.
In recent years, the size of toner particles is being reduced in order to improve resolution and precision detail, and also many proposals have been made regarding rounded toner wherein the form of the toner particles is spherical, in order to improve transfer efficiency and flowability. For example, Japanese Patent Laid-Open No. 56-13945 discloses a method wherein a disk or multi-fluid nozzle is used to mist a molten mixture into the air, thereby obtaining rounded or spherized toner, but this method has problems regarding reduction of particle diameter.
Further, rounded toner particles can be manufactured by methods described in Japanese Patent Publication No. 36-10231, Japanese Patent Laid-Open No. 59-53856, and Japanese Patent Laid-Open No. 59-61842, such as methods for generating rounded toner particles by the suspension polymerizing method; the emulsion polymerizing method which is represented by the soap-free polymerizing method wherein polymerization is directly performed in the presence of an aqueous polar polymerization initiator, thereby obtaining rounded toner particles; or the dispersion polymerizing method wherein a solvent is used in which monomers are soluble but polymers are non-soluble, and toner particles are formed in this solvent. However, with each of these polymerizing methods, the binder resin included in the toner is restricted to vinyl resins.
Japanese Patent Laid-Open No. 4-303849 and Japanese Patent Laid-Open No. 8-211655 propose using the reverse-phase sedimentation method wherein water is added to a polyester resin solution. However, this method is restricted to polyester resin for the binder resin comprising the toner. Further, the above method involves dissolving the binder resin component with an organic solvent which is water-immiscible, into which pigments and other additives are dissolved and/or dispersed to form a liquid into which droplets or water are dropped, thereby obtaining rounded toner, so there is a problem in that great amounts of organic solvent must be used as to the resin component and maintain a state wherein sufficient fluidity is secured, as rounded toner cannot be obtained otherwise.
Further, with the method described in Japanese Patent Laid-Open No. 8-248680 as well, the binder resin component is dissolved with an organic solvent which is water-immiscible, and this solution is dispersed in an aqueous phase to form oil droplets, so there is a problem in that great amounts of organic solvent must be used to obtain sufficient fluidity.
Efforts are being made to create rounded or spherical toner by taking the pulverized toner obtained by the aforementioned common pulverization method and spherizing this toner either mechanically or by heat, but much time or energy must be spent in order to obtain truly spherical toner with such methods, so these methods are not economically feasible.
Japanese Patent Laid-Open No. 8-179553 and Japanese Patent Laid-Open No. 9-34167 disclose a method for producing toner, comprising the steps of: dispersing fine particles containing binder resin and coloring agent into an aqueous medium including a dispersant which is solid at room temperature, thus preparing a particle disperse liquid; mixing the obtained particle disperse liquid with a solvent disperse liquid which is water-immiscible, this solvent disperse liquid having been prepared by dispersing a hydrophobic solvent into an aqueous disperse liquid; and removing the hydrophobic solvent by heating and/or depressurizing the obtained mixed liquid, thereby forming particles into spherical or deformed shapes.
However, these Publications describe embodiments wherein the above particle disperse liquid and the solvent disperse liquid which is water-immiscible are mixed by adding the solvent disperse liquid which is water-immiscible to the particle disperse liquid, so coagulation of the fine particles in the particle disperse liquid readily occurs due to so-called solvent shock. In this process a problem occurs in that the obtained toner particles tend to become coarser and broadening of the particle distribution tends to occur.
As described above, there has not yet been discovered a method whereby spherical toner can easily be produced regardless of the resin component comprising the toner, and free of increase in particle size distribution and occurrence of coarse particles.